In the field of medicine, in order to detect electrical signals such as brain waves output from biological tissues, electrodes to be used by being attached to a living body or being embedded in the living body have been utilized. As such an electrode, a pin support-shaped electrode array inserting a plurality of electrode elements composed of platinum or gold into the biological tissue has been known (for example, Patent Document 1). However, since such a highly invasive method imposes a heavy burden on the living body, there has been a demand for a measurement method with fewer burdens.
Accordingly, minimally invasive methods that do not insert the electrode elements into the living body have been developed. For example, in Patent Document 2, an electrode realizing minimal invasion by using a fine metal wire as the electrode element has been described. For example, although an electrode element made of a metal such as platinum or gold is basically harmless to the human body, when being brought into direct contact with the body tissues or cells, a defense reaction (inflammatory reaction) occurs between the electrode element and the tissue due to the antibody response of biological cells. For this reason, it is difficult to observe biological information for a prolonged period. In addition, there is a problem of heavy damage to the living body due to friction when a hard metal is rubbed inside the soft body.
In order to prevent such a problem, it is considered to place a material having biocompatibility between the electrode element and the biological tissue, thereby preventing the direct contact between the electrode element and the biological tissue.
However, in the electrode in which a plurality of electrode elements are arranged, there is a problem in that sensitivity is lowered due to the occurrence of leakage of signals between the electrode elements (crosstalk). Therefore, in order to obtain the electrical signals in the body with high sensitivity and high accuracy, it is necessary to provide an insulating wall between the electrode elements. Since this type of insulating wall also comes into contact with the living body, it is preferably formed of a highly biocompatible material, and insulating walls using silicone elastomers have been studied.
For example, in Non-Patent Document 1, a technique for forming an insulating wall made of silicone around the electrode elements has been described. The insulating wall made of silicone is obtained by coating an upper portion of the electrode element on the electrode substrate with a photoresist, spin-coating a thermosetting silicone prepolymer thereon, followed by heating to cure a polysiloxane compound, and then removing the photoresist. In Non-Patent Document 2, formation of an insulating portion of the electrode through a photolithography method employing photopolymerization by spin-coating a polysiloxane compound with a terminal vinyl ether group on the electrode substrate has also been described.